1. Field of the Invention
The present invention relates to an amplification type solid state imaging device. More particularly, the present invention relates to the exposure time control and the shutter operation for an amplification type solid state imaging device.
2. Description of the Related Art
An amplification type solid state imaging device having a plurality of pixels each of which is formed by a photodiode and a MOS transistor has been known in the art.
A conventional amplification type solid state imaging device has a plurality of pixels arranged in a matrix. Each pixel includes: a photodiode for photoelectric conversion; a signal amplification MOS transistor which functions as an amplifier for amplifying a change in the potential of the photodiode; a pixel selection MOS transistor; and a reset MOS transistor for resetting the potential of the photodiode to a predetermined initial potential. The gate terminals of the selection MOS transistors of the pixels along each row are commonly connected to a row line, and a predetermined signal read pulse is applied to these gate terminals. The gate terminals of the reset MOS transistors of the pixels along each row are commonly connected to a row line, and a predetermined reset pulse is applied to these gate terminals via a row line. Terminals on one end of the selection MOS transistors of the pixels along each column are commonly connected to a column line to form a column line. The amplification type solid state imaging device performs a shutter reset operation by applying a shutter operation reset pulse to the gate terminals of the reset MOS transistors during a period which is different from the period during which the reset pulse is applied to the gate terminals of the reset MOS transistors.
However, when a shutter reset operation is performed on the pixels along the (i+1)th row while, at the same time, the pixels along the ith row (from which image signals are being read out) are imaging a high brightness object, the potential of a column line to which signals from the pixels along the ith row are applied decreases. Therefore, the reference potential of the photodiode of a pixel along the (i+1)th row shifts from the intended level after the shutter reset operation. Thus, ghost noise appears on the screen which displays the image taken by the solid state-imaging device.
According to one aspect of this invention, there is provided an amplification type solid state imaging device, including a plurality of pixels arranged in a matrix each of which includes: a photodiode for photoelectric conversion; a signal amplification MOS transistor which functions as an amplifier for amplifying a change in the potential of the photodiode; a pixel selection MOS transistor; and a reset MOS transistor for resetting the potential of the photodiode to a predetermined initial potential, gate terminals of the selection MOS transistors of the pixels along each row being commonly connected together with a predetermined signal read pulse being applied to the gate terminals, gate terminals of the reset MOS transistors of the pixels along each row being commonly connected together with a predetermined reset pulse being applied to the gate terminals, and terminals on one end of the selection MOS transistors of the pixels along each column being commonly connected together to form a signal line, wherein a shutter reset operation is performed by applying a shutter operation reset pulse to the gate terminals of the reset MOS transistors during a period which is different from a period during which the reset pulse is applied to the gate terminals of the reset MOS transistors in a pixel signal read operation, wherein the shutter operation reset pulse is applied to the gate terminals of the reset MOS transistors in a state where a potential of the signal line is set to a predetermined fixed potential.
In one embodiment of the invention, the shutter operation reset pulse is applied to the gate terminals of the reset MOS transistors during a period immediately after a reset signal read period in the pixel signal read operation.
In one embodiment of the invention, the amplification type solid state imaging device includes fixed potential supply means for supplying the predetermined fixed potential to the signal line, wherein the shutter operation reset pulse is applied to the gate terminals of the reset MOS transistors by the fixed potential supply means in a period during which the fixed potential is supplied to the signal line.
In one embodiment of the invention, the fixed potential is supplied to the signal line by the fixed potential supply means in a period during which the reset pulse is applied to the gate terminals of the reset MOS transistors in the pixel signal read operation for a given row; and the shutter operation reset pulse is applied in said period to the gate terminals of the reset MOS transistors of the pixels along a different row.
Thus, the invention described herein makes possible the advantages of providing an amplification type solid state imaging device capable of obtaining a uniform image without ghost noise due to a shutter reset operation.
This and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.